Field of the Invention and Related Art Statement
This invention relates to an endoscope light source apparatus provided with a means of controlling an illuminating light amount to an object to be imaged.
In an endoscopic observation, an exclusive light source apparatus is used so that an illuminating light from the light source apparatus may be radiated onto an object to be imaged from a tip of an endoscope through light guide fibers within the endoscope. In order to adjust the illuminating light amount in response to the brightness (reflection factor) of the object to be imaged, a diaphragm blade is provided between a connector with the endoscope and a lamp within the light source apparatus. A slitted plate or honeycomb plate provided rotatably with the axis intersecting at right angles with a light path as a center is used for such a diaphragm blade. That is to say, by electrically or mechanically rotating this diaphragm blade, the light intercepting rate can be varied to adjust the light amount incident upon the light guide. A related art example using a honeycomb diaphragm is mentioned in a Japanese patent application No. 173832/1984.
The endoscope light source apparatus of the above mentioned related art example shall be explained with reference to FIG. 1. Here, a so-called electronscope in which a solid state imagining device is built within the tip part of an insertable part to image an object shall be explained. A light source apparatus 102 is connected to an electronscope 100. The electronscope 100 is provided with a light guide 106 consisting of an optical fiber bundle leading an illuminating light radiated from the light source apparatus to the tip of the insertable part to illuminate an object 104 and a charge coupled device (CCD) 108 as a solid state imaging device built within the tip part.
The light source apparatus 102 is provided with a light source such as, for example, a lamp (xenone lamp) 110. The lamp 110 is regulated to be of a constant current so that, when an output signal of a pulse generating circuit 172 is input into a current regulating circuit 114, a flash will be emitted as synchronized with the signal. A switching circuit 116 is connected to the current regulating circuit 114 to form a light source lighting circuit 118.
The light emitted from the lamp 110 is incident upon the light guide 106 of the electronscope 100 through a diaphragm blade 120, optical lens system 122 and rotary filter 124. The diaphragm blade 120 is rotated by a driving device 126 and consists of a slitted plate or honeycomb plate variable in the inclination with the light path. The rotary filter 124 is rotated by a motor 128 and colors the illuminating light in red(R), green (G) adn blue (B) in turn. There is a light intercepting period between the exposure periods of the respective color components. An optical sensor 130, detecting the exposure periods of the respective color components of the rotary filter 124, is provided. When the exposure periods of the respective color components end, a pulse will be output from the optical sensor 130 and will be fed to a color signal synchronizing circuit 132. After a predetermined period (corresponding to the light intercepting period) from this synchronizing pulse, only for a fixed period (corresponding to the exposure period), the color signal syncrhonizing circuit 132 feeds a color synchronizing signal to the pulse generating circuit 112 so that the lamp 110 may be synchronized with the rotation of the rotary filter 124 and may emit a light only in the exposure periods of the respective colors.
The output signal of the CCD 108 is fed to the light source device 102 side through a signal line and connector 138 within the electronscope 100 and is input into a signal processing circuit 140 making an amplification, clamping and various corrections. The output of the signal processing circuit 140 is fed to a video circuit 142 and a picture image is output in a displaying part (not illustrated). The output of the signal processing circuit 140 is input also into a differential amplifier 144. The standard signal of the differential amplifier is given by a standard voltage circuit 146. The output of the differential amplifier 144 regulates the diaphragm driving device 126.
An integrator is also provided within the signal processing circuit so that the illuminating light amount may be detected. The difference between this light amount value and the standard signal is operated by the differential amplifier 144. In response to this result, the diaphragm driving device 126 is regulated. Thereby, the diaphragm blade 120 will be inclined in the direction of intercepting the light in case the illuminating light is too bright and will be inclined in the direction of opening the light path in case the illuminating light is too dark. This automatic light adjusting operation is the same not only in an electronscope but also in an ordinary fiberscope.
In a conventional light source apparatus for endoscopes, the diaphragm blade is exclusively for adjusting the light, the driving mechanism is for rotating the diaphragm blade and their control circuit are separately required. Therefore, defects have caused the number of the component parts to increase and has caused the light source apparatus to become large, complicated and costly.
Now, in an electronic endoscope apparatus using a field sequential system, in order to improve the color reproductivity of an endoscope picture image, it is necessary to adjust the color balance (white balance) of R, G and B in advance. In the case of using, for example, as a prior art example, the rotary filter 2 provided with respective R, G and B color transmitting filters 1R, 1G and 1B as shown in FIG. 2 for a light source emitting a continuous light, there is used a method of adjusting the aperture ratio of the respective R, G and B color transmitting filters 1R, 1G and 1B by using the light intercepting member 3. Even if the aperture rates of the respective R, G and B color transmitting filters 1R, 1G and 1B are set in advance, depending on the dispersion of the imaging device or the like, it can not be said that the best state can always be held. In such a case, a light intercepting member is further added to the aperture surface of the filter set in advance.
In this prior art example, even if the aperture rates of the respective color transmitting filters are set in advance, due to the dispersion of the imaging device or the like, the aperture rates of the respective color filters must be readjusted by using a light intercepting member. In such a case, defects occur where no accurate color balance adjustment can be made, a light intercepting member is required and a large amount of time is needed for the adjustment.
When a flash light source is used (which shall be referred to as a strobo lamp hereinafter), and when the energy fed to the strobo lamp is made variable, the emitted light amount can be adjusted. Therefore, when proper energy is fed to the strobo lamp to emit a light within the aperture time of the respective R, G and B color filters as shown in FIG. 3a, the R, G and B color balance can be adjsuted the same as in the above mentioned example.
In order to make the fed energy variable, there is adopted a method wherein the number of times of the strobe light emission is made variable during the aperture time of the respective color filters is made variable is made variable.
In the method wherein the number of times of the light emission of the strobo lamp during the aperture periods of the respective color filters is thus controlled, it is necessary to expand the control range by increasing the number of times of the light emission of the strobo lamp which therefore causes a defect in that the life of the strobo lamp is extremely reduced.
Also, as disclosed in a Japanese patent laid open No. 205884/1984 (or U.S. Pat. No. 4,532,918), there is adopted a method wherein the condenser capacity, represented by the formula of Energy E=1/2 CV.sup.2, and the applied voltage V are adjusted.
In this prior art example, the energy fed to the strobo lamp must be made variable during the aperture time of the respective R, G and B colors which therefore causes defects in that the control circuit is complicated and costly.